In many manufacturing processes, the ability to repeatedly and uniformly cure a polymer system is highly important, if not critical, to the resultant product. Heretofore, methods for determining the degree of cure were not only time consuming, but were also destructive and could not be applied as an "in-line" process. Examples of such prior art methods are solvent extraction of the polymerized film wherein the quantity of uncured material which is dissolved in the solvent is measured and compared with the total weight of cured and uncured polymer to calculate the % Sol; and glass transition temperature (T.sub.g) determinations of the polymer wherein the T.sub.g is directly related to the extent of polymerization.
A major concern in the manufacture of high density multilayer printed wiring boards employing a thin photodefinable polymeric dielectric film to separate conductive layers is the ability to inspect the board prior to operations such as lamination, circuit formation and solder mask application to insure uniformity from board to board and to insure the proper degree of cure has been attained. Conductive paths in the various layers are selectively interconnected by photodefined microvias in the dielectric. The degree of cure achieved in these photodefinable dielectric layers is critical to the proper operation of the multilayer printed circuit board. Also, the ability to successfully inspect the degree of cure of the photodefinable polymer layers used in such boards allows for processing and/or repair schemes which can result in increased product yields.
We have now discovered a non-destructive, optical means, for determining the extent of cure of a polymer which can be operated as an on-line, real-time test during a manufacturing process and can be used to control the process.